1. Field of the Invention
The present invention relates to an electron beam exposure mask, an electron beam exposure method, and an electron beam exposure system, which correct a proximity effect in an electron beam exposure.
2. Description of the Prior Art
In recent years, electron beam exposure systems have come to be used in order to form fine patterns in lithography processes in the manufacture of semiconductor devices and the like.
It is known that, in an electron beam exposure system, there occurs a phenomenon in which line widths and the like of a pattern transferred onto resist deviate from the designed values because of influences of a so-called proximity effect in which incident electrons are scattered in the resist.
For example, when an exposure and development are performed using a line-and-space mask pattern 1 such as shown in FIG. 1A, the shapes of patterns 2 in a peripheral portion become small as shown in FIG. 1B though they have the same size as other patterns on a mask. This is because the amounts of energy received from the back scattering of incident electrons are different between inner patterns and peripheral patterns as shown in the accumulated energy distribution of FIG. 1C. FIG. 1C shows accumulated energies 3 to 4 in which the dose of a primary beam is superimposed on an accumulated energy 6 resulting from the back scattering of incident electrons. In the case of a constitution including regularly repeated patterns as in this example, the influence of the proximity effect of back scattering is saturated and equalized in an inner portion of a writing region. However, as shown in FIG. 1C, a peripheral portion has a distribution having a slope in which an accumulated energy decreases with increasing distance from a center portion.
In the case where a wafer given an accumulated energy such as shown in FIG. 1C is developed, if a threshold is assumed to be, for example, the line 5, then developed line widths are determined at positions where the threshold 5 and the energies 3 to 4 from a primary beam intersect. Accordingly, as shown in FIG. 1B, line widths are different between an inner portion and a peripheral portion of a device formation pattern.
Various methods of correcting the above-described proximity effect are being studied. For example, Japanese Unexamined Patent Publication No. Hei 5-335221 discloses an exposure method in which so-called GHOST exposure is applied to cell projection method. Here, GHOST exposure is a method which corrects a proximity effect by performing an exposure in such a manner that an auxiliary exposure pattern is superimposed on a peripheral portion of a desired device formation pattern.
Further, Japanese Unexamined Patent Publication No. 2003-332225 discloses a proximity effect correction method including the steps of: checking exposure data dimensions found based on an exposure intensity distribution function or requirements for the manufacture of a device and a mask against existing mask data; determining correction exposure data based on the result of the checking; and creating a correction light exposure by calculating an exposure intensity and a back scattering intensity using the correction exposure data dimensions.
Heretofore, in a peripheral portion of a device formation pattern in which an accumulated energy is small, patterns have been written by changing irradiation time for each pattern by variable-shaped exposure so that accumulated energies in an inner portion and a peripheral portion become equal. In this case, since variable-shaped exposure is used, the patterns are individually exposed to light, and an enormous amount of time is needed compared to that for cell projection method.
However, in the cell projection method, patterns have to be simultaneously transferred. Accordingly, it is substantially impossible to change irradiation time for each individual pattern in a peripheral portion of a device formation pattern to obtain an accumulated energy equivalent to that of an inner portion.
Further, in the method described in Japanese Unexamined Patent Publication No. Hei 5-335221, a proximity effect is corrected by exposing an auxiliary pattern to light outside a device formation pattern. Accordingly, if there is no space for that, correction cannot be performed. Additionally, though an auxiliary light exposure is determined depending on the device formation pattern, it is difficult to equalize an energy in a pattern existing in a portion in which an accumulated energy is inclined in a peripheral portion with an energy equivalent to that in an inner portion.
Moreover, in the method described in Japanese Unexamined Patent Publication No. 2003-332225, correction exposure data is not calculated for each individual pattern existing in a portion in which an accumulated energy is inclined in a peripheral portion of a device formation pattern, but an auxiliary light exposure is calculated by selecting a representative pattern. Accordingly, it is impossible to perform an exposure so that all patterns existing in the peripheral portion can be formed into desired shapes.